Optically detected electron paramagnetic resonance by microwave modulated magnetic circular dichroism

Electron paramagnetic resonance (EPR) can be detected optically, with a las er beam propagating perpendicular to the static magnetic field. As in conve ntional EPR, excitation uses a resonant microwave field. The detection proc ess can be interpreted as coherent Raman scattering or as a modulation of t he laser beam by the circular dichroism of the sample oscillating at the mi crowave frequency. The latter model suggests that the signal should show th e same dependence on the optical wavelength as the MCD signal. We check thi s for two different samples [cytochrome c-551, a metalloprotein, and ruby ( Cr3+:Al2O3)]. In both cases, the observed wavelength dependence is almost i dentical to that of the MCD signal. A quantitative estimate of the amplitud e of the optically detected EPR signal from the MCD also shows good agreeme nt with the experimental results. (C) 1999 American Institute of Physics. [ S0021-9606(99)00842-9].